Retinoscope with magnetic coupling

ABSTRACT

A streak retinoscope projects an elongate patch of light onto the retina of an eye under examination. A housing ( 1 ) contains means for rotating the patch relative to the eye and adjustable focusing means for focusing the patch on the eye. Both the rotation means and the focusing means are adjusted by a single control member, such as sleeve ( 62 ), which encircles at least part of the housing member. The control member is coupled at least to the rotation means (and preferably also to the focusing means) by a magnetic linkage so as to permit rotation of the control member on the housing through at least one full revolution.

FIELD OF THE INVENTION

This invention relates to retinoscopes, and more specifically to streakretinoscopes.

BACKGROUND TO THE INVENTION

Retinoscopy is a technique which employs a retinoscope to provide anobjective indication of the refractive error of an eye. A retinoscopeprojects a patch of light onto the retina of an eye under examination,whilst permitting a user of the device to observe that patch. A streakretinoscope projects an elongated patch of light onto the eye, andincludes a mechanism for rotating and focusing the patch. The rotationof the patch is used in the measurement of the axis of astigmatism of aneye under examination.

In a typical retinoscope, light emitted by a source passes through afocusing lens system, and is then reflected by an angled, half silveredor apertured mirror into the eye under observation. The image of thepatch of light on the eye is viewed by the user from the opposite sideof the mirror. The retinoscope also has a facility for moving the lenssystem to alter the focus (ie the vergence) of the patch of light on theretina of an eye under observation.

For ease of use, some retinoscopes have a single dual action controlmember for rotating the patch of light and for altering the position ofthe lens system. Such a member may, for example, comprise a rotarysleeve directly connected to the lens system and to a holder for a lightsource for the retinoscope. The sleeve is usually accessible throughcut-outs in the outer housing of the retinoscope. Although the sleeve ofthis design can rotate through a full 360°, the portions of the bodybetween the cut-outs limit the positions on the retinoscope at which theuser can hold the sleeve. Other types of retinoscope have a sleeve whichencircles the retinoscope housing, and is directly linked to the lampholder and lens system through apertures in the housing. Whilst thisarrangement provides a user with access to the sleeve through a full360°, the cut-outs in the housing limit the extent of availablerotational movement.

Other designs of retinoscope avoid this limitation by connecting anexternal sleeve, which encircles the retinoscope, to a lamp holderthrough a system of gears, but such an arrangement is relativelycomplicated and results in the patch of light being rotated in theopposite sense from the sleeve.

SUMMARY OF THE INVENTION

According to the invention, there is provided a streak retinoscope forprojecting an elongate patch of light onto the retina of an eye underexamination, the retinoscope comprising housing means, rotation meanscontained within the housing means and operable to rotate the patchrelative to said eye, adjustable focusing means for focusing said patchon said eye, and a dual action external control member, which encirclesat least part of the housing member, for operating the rotation meansand adjusting the focusing means, wherein the control member is coupledto the rotation means by a magnetic linkage so as to permit rotation ofthe control member relative to the housing means through at least onefull revolution.

Since the housing means is encircled by the control member, it does notimpede access to the latter. Furthermore, the magnetic linkage enablesthe control member to move the rotation means without making directmechanical contact with the latter, and thus avoids the need for anyconnecting gears or connections which limit the amount of allowablerotation of the control member.

Preferably, the control member is rotatably mounted on the housingmeans, and is also slidable therealong, the arrangement being such thatrotation of the member operates the rotation means, whilst slidingmovement of the member adjusts the focusing means.

Preferably, the magnetic linkage couples the control member to both therotation means and the focusing means.

Preferably, the magnetic linkage comprises a first set of magnetsconnected to the control member (at angularly fixed positions relativethereto) and a second set of magnets connected to the rotation means (atangularly fixed positions) and to the focusing means. Thus, the magneticlinkage also avoids the need to provide a mechanical connection betweenthe control member and the focusing means. Consequently, the focusingmeans and rotation means can both be situated wholly within the housingmeans, whilst the control member can be situated entirely outside thehousing means.

Preferably, each set of magnets lies on a respective annular path, thetwo annular paths preferably being substantially concentric.

Preferably, the orientations of the magnets are such that any angulardisplacement of the first set of magnets relative to the second resultsin the exertion on the second set of magnetic attractive and repulsiveforces tending to move the second set into its original angular positionrelative to the first set.

To that end, the polar orientations of the magnets in each set relativeto the positions of the magnets in the other set preferably alternate.

Preferably, each magnet is so positioned that one of its poles faces theother set, and in this case, for each magnet, the pole facing the otherset is of the opposite polarity to the correspondingly positioned poleof each of its immediate neighbours in its set.

Thus, for example, a magnet in the first set which is positioned withits north pole facing radially inwards towards a second set will besituated between two immediately neighbouring magnets, of the first set,whose south poles face radially inwards.

Preferably, there are six magnets in each set.

Preferably, the rotation means-causes the patch of light to rotate byrotating a lamp, and may therefore to advantage comprise a rotatablelamp holder and a rotatable inner sleeve which is angularly fixed tosaid holder and which carries said second set of magnets.

Conveniently, the control member comprises a cylindrical sleeve, on theinner periphery of which the magnets of said first set are mounted.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 is a partially cut-away side view of a streak retinoscope inaccordance with the invention; and

FIG. 2 is a sectional side view, from the opposite side, of the streakretinoscope.

DETAILED DESCRIPTION

The streak retinoscope shown in the drawings has a housing comprising acylindrical body 1 of a non ferromagnetic material (for examplealuminium) which contains a lamp body 2 which carries having a halogenlight bulb 4 having an elongate filament (not shown). In use, lightemitted by the filament passes through a vergence lens system 6 situatedtowards the top of the body 1 and into a head 8. The head 8 is identicalto the head used in the KEELER VISTA STREAK retinoscope, and includes anangled half-silvered or apertured mirror 9 which reflects lighttravelling up from the lens 6 through 90° to exit the head 8 through anaperture 11 in the front 10 thereof and into the eye under examination(not shown). The retinoscope forms an image of the filament of the bulb4 on the eye under examination, and thus projects an elongate streak oflight onto that eye. The image is viewed by the user of the retinoscopethrough the mirror 9 and a rear aperture 12. The housing alsoaccommodates a plate which is moved by means of a button 14 and whichincludes two apertures, of different diameters, either of which can beselectively positioned in the viewing path from the mirror to the userto cause a selected degree of partial occlusion of the aperture 12 tooccur.

The head is also equipped with an orbital/brow rest 15. The features ofthe head 8 are not described in detail because they are already knownfrom the KEELER VISTA STREAK retinoscope.

The head 8 has a collar 16 which is externally screw-threaded and isscrewed onto the top of the body 1. The bottom of the body 1 isexternally screw-threaded so as to receive and retain a base cap 18. Thebase cap 18, in turn, includes a screw-threaded connector 20 forattachment to a handle (not shown), such as is used on the KEELER VISTASTREAK retinoscope, which handle also contains batteries for operatingthe lamp 2. The base cap 18 includes a through bore through which thelamp body 2 extends.

The bottom of the body 2, referenced 24, includes terminals forconnecting the lamp 2 and hence the bulb 4 to a battery power supply inthe handle. The lamp body 2 is securely held within an annular lampholder 26 by means of an “O”-ring 27. The lamp holder 26 has anupstanding cylindrical wall 28 which defines a central passage 30 whichaccommodates the upper portion of the lamp. At the bottom of the wall28, the holder 26 has a radial flange 36. The flange 36 is situatedbelow a circlip 34 which sits in an annular groove on the inside of thebody 1.

When the handle 21 is attached, the terminals in the handle make contactwith the bottom 24 and exert an upward biasing force on the lamp 22, andhence on the holder 26. The flange 36 defines an annular upward shoulder38 which is therefore urged against three balls 68, held in a race 40which is in turn urged up against a thrust washer 42 located against theunderside of the circlip 34. The lamp holder 26 also extends through theconnector 20. The dimensions of the lamp holder are such that it, andhence the lamp body 2 (and bulb 4), is rotatable within the body 1 aboutthe elongate axis of the latter.

A stop ring 31 is attached to the top of the wall 28, and serves to cutdown glare from the edge of the bulb in the projected image.

The wall 28 of the lamp holder 26 includes an axial slot 44 into which apeg 46 extends (FIG. 2). The peg 46 projects radially inwards from aninner sleeve 48, which is rotatably retained in the body 1. The peg 46provides a rotational key between the lamp holder 26 and the innersleeve 48.

The inner sleeve 48 is also axially slidable along the inside of thebody 1 and defines a central passage 50 for light from the bulb 4. Theinner sleeve 48 also includes six equi-angularly spaced recesses in itsouter surface. One such recess is shown at 52. Each of these recessesaccommodates a respective rare earth magnet, such as the magnet 54. Eachmagnet is arranged with one pole facing radially outwards and the otherradially inwards. Furthermore, the polar orientations of the magnetsalternate so that each magnet which is orientated with its north polefacing outwards is positioned between two immediately neighbouringmagnets which are positioned with their south poles facing outwards, andvice versa.

The outer surface of the sleeve 48 is also provided with an annulargroove which accommodates a split washer 56 which, in use, presents agreater resistance to sliding of the sleeve 48 along the body 1 than itdoes to rotation of the sleeve 48 about the axis of the body 1. The topof the inner sleeve 48 includes a reduced diameter cylindrical portion58 which extends upwards from an annular step 60, and to which the lens6 is adhered.

The inner sleeve 48, and hence the lamp 22 and the lens 6 can be rotatedand moved axially along the body 1 by means of a control membercomprising an external sleeve 62 which is slidably and rotatably mountedon the exterior of the housing 1.

The sleeve 62 includes a trim ring 64 below which six rare earth magnetssuch as the magnet 66 are accommodated by the sleeve 62. The ringcontains six magnets, each of which cooperates with a respectivecorresponding magnet mounted on the sleeve 48, and is in angularregistry with the corresponding magnet in the sleeve 48. To that end themagnets are arranged in an annular formation, with the pole of eachmagnet which faces radially inwards being opposite to the pole of thecorresponding magnet on the sleeve 48. Thus, a magnet in the sleeve 62which is in angular registry with, and therefore cooperates with, amagnet (on the sleeve 48) orientated with its south pole facingoutwards, will be arranged with its north pole facing radially inwards.

It will be seen that the magnets in the sleeve 62 and those mounted onthe sleeve 48 provide a coupling between the sleeve 62 and sleeve 48which acts through the wall of the body 1, and therefore avoidsrequirements for any apertures in the body 1 to provide a directmechanical connection between the two components.

Also, since the sleeve 62 encircles the body 1, access to the sleeve 62is not restricted by any part of the body 1.

In use, the orientation of the bulb 4 (and hence of the streak projectedonto the eye under examination) is adjusted by rotating the sleeve 62about the exterior of the body 1. This causes the magnets in the sleeve62 to act on the magnets in the sleeve 48 so as to cause a correspondingrotation of the sleeve 48, and hence the lamp body 2 and lens system 6.While this happens, the split washer 56 prevents the sleeve 48 fromsliding along the inside of the body 1 (and thus from altering the focusof the image on the eye under examination). If the focusing provided bythe vergence lens 6 is to be adjusted, the sleeve 62 is slid axiallyalong the housing 1, causing a similar axial movement of the innersleeve 48, and hence the lens 6.

If, during rotational movement, the inner sleeve 48 and outer sleeve 62begin to move out of registry with each other, then the attractiveforces between each magnet in the ring 64 and its corresponding magneton the sleeve 48 are supplemented by repulsive forces between eachmagnet in the ring 64 and one of the neighbours of the correspondingmagnets on the sleeve 48. It will be appreciated that the rotation ofthe sleeve 62 causes the streak projected by the retinoscope to rotatein the same sense.

What is claimed is:
 1. A streak retinoscope for projecting an elongatepatch of light onto the retina of an eye under examination, theretinoscope comprising housing means, rotation means contained withinthe housing means and operable to rotate the patch relative to said eye,adjustable focusing means for focusing said patch on said eye, and adual action external control member, which encircles at least part ofthe housing member, for operating the rotation means and adjusting thefocusing means, wherein the control member is coupled to the rotationmeans by a magnetic linkage so as to permit rotation of the controlmember relative to the housing means through at least one fullrevolution.
 2. The retinoscope according to claim 1, in which thecontrol member is rotatably mounted on the housing means, and is alsoslidable therealong, the arrangement being such that rotation of themember operates the rotation means, whilst sliding movement of themember adjusts the focusing means.
 3. The retinoscope according to claim2, in which the magnetic linkage couples the control member to both therotation means and the focusing means.
 4. The retinoscope according toclaim 1, in which the magnetic linkage comprises a first set of magnetsconnected to the control member at angularly fixed positions relativethereto and a second set of magnets connected to the rotation means atangularly fixed positions and to the focusing means.
 5. The retinoscopeaccording to claim 4, in which the focusing means and rotation means areboth situated wholly within the housing means, whilst the control memberis situated entirely outside the housing means.
 6. The retinoscopeaccording to claim 4, in which each set of magnets lies on a respectiveannular path, the two annular paths being substantially concentric. 7.The retinoscope according to claim 6, in which the orientations of themagnets are such that any angular displacement of the first set ofmagnets relative to the second results in the exertion on the second setof magnetic attractive and repulsive forces tending to move the secondset into its original angular position relative to the first set.
 8. Theretinoscope according to claim 7, in which the polar orientations of themagnets in each set relative to the positions of the magnets in theother set alternate.
 9. The retinoscope according to claim 8, in whicheach magnet is so positioned that one of its poles faces the other set,and for each magnet the pole facing the other set is of the oppositepolarity to the correspondingly positioned pole of each of its immediateneighbours in its set.
 10. The retinoscope according to claim 9, inwhich there are at least six magnets in each set.
 11. The retinoscopeaccording to claim 4, in which the rotation means causes the patch oflight to rotate by rotating a lamp, and comprises a rotatable lampholder and a rotatable inner sleeve which is angularly fixed to saidholder and which carries said second set of magnets.
 12. A retinoscopeaccording to claim 1, in which the control member comprises acylindrical sleeve, on the inner periphery of which the magnets of saidfirst set are mounted.